Recent years have witnessed practical use of a flat-panel display in various products and fields. This has led to a demand for a flat-panel display that is larger in size, achieves higher image quality, and consumes less power.
Under such circumstances, great attention has been drawn to an organic EL display device that (i) includes an organic electroluminescence (hereinafter abbreviated to “EL”) element which uses EL of an organic material and that (ii) is an all-solid-state flat-panel display which is excellent in, for example, low-voltage driving, high-speed response, and self-emitting.
An organic EL display device includes, for example, (i) a substrate made up of members such as a glass substrate and TFTs (thin film transistors) provided to the glass substrate and (ii) organic EL elements provided on the substrate and connected to the TFTs.
An organic EL element is a light-emitting element capable of high-luminance light emission based on low-voltage direct-current driving, and includes in its structure a first electrode, an organic EL layer, and a second electrode stacked on top of one another in that order, the first electrode being connected to a TFT. The organic EL layer between the first electrode and the second electrode is an organic layer including a stack of layers such as a hole injection layer, a hole transfer layer, an electron blocking layer, a luminescent layer, a hole blocking layer, an electron transfer layer, and an electron injection layer.
A full-color organic EL display device typically includes organic EL elements of red (R), green (G), and blue (B) as sub-pixels aligned on a substrate. The full-color organic EL display device carries out an image display by, with use of TFTs, selectively causing the organic EL elements to each emit light with a desired luminance.
Such an organic EL display device is produced through a process that forms, for each organic EL element serving as a light-emitting element, a pattern of a luminescent layer made of an organic luminescent material which emits light of at least the above three colors (see, for example, Patent Literatures 1 to 3).
Such formation of a luminescent layer pattern is performed by a method such as (i) a vacuum vapor deposition method that uses a vapor deposition mask referred to as a shadow mask, (ii) an inkjet method, and (iii) a laser transfer method.
The production of, for example, a low-molecular organic EL display (OLED) has conventionally used a vapor deposition method involving a shadow mask, the vapor deposition method forming organic layers by selective application.
The vacuum vapor deposition method involving a shadow mask uses a shadow mask (full-cover contact type shadow mask) that is so sized as to allow vapor deposition to be performed throughout the entire vapor deposition region of a substrate. The shadow mask is typically equivalent in size to the substrate.
FIG. 24 is a cross-sectional view schematically illustrating a configuration of a conventional vapor deposition device involving a shadow mask.
The vacuum vapor deposition method involving a shadow mask, as illustrated in FIG. 24, forms a pattern by (i) placing a substrate 301 and a vapor deposition source 302 at such positions that the substrate 301 and the vapor deposition source 302 face each other, (ii) forming, in a shadow mask 303, openings 304 corresponding to a pattern of a portion of a target vapor deposition region so that no vapor deposition particles are adhered to a region other than the vapor deposition region, and (iii) depositing vapor deposition particles onto the substrate 301 through the openings 304.
The substrate 301 is placed in a vacuum chamber (not shown). The vapor deposition source 302 is fixed below the substrate 301. The shadow mask 303 is either fixed at a certain interval from the substrate 301 or moved relative to the substrate 301 while the substrate 301 and the vapor deposition source 302 are fixed to an inner wall of the vacuum chamber.
Patent Literature 1, for example, discloses a method that involves a load-lock vapor deposition source, the method (i) aligning a mask and a substrate with each other, next (ii) performing vacuum vapor deposition of a first luminescent material from directly below the substrate to form an arrangement of first light-emitting sections each substantially identical in shape to an opening of the mask, then (iii) shifting the mask, and (iv) performing vacuum vapor deposition of a second luminescent material from directly below the substrate to form an arrangement of second light-emitting sections each substantially identical in shape to the opening of the mask.
Patent Literature 2 discloses a method involving a partition wall that is so provided on a substrate to which display electrodes are provided as to protrude from the substrate and surround the display electrodes, the method (i) placing a mask on a top surface of the partition wall, (ii) depositing an organic EL medium on the display electrodes surrounded by the partition wall, then (iii) shifting the mask so that an opening of the mask is shifted from the position directly above a display electrode to the position directly above an adjacent display electrode, thereby sequentially forming luminescent layers each substantially identical in shape to the opening of the mask.
The vacuum vapor deposition method involving a shadow mask is used not only to form a luminescent layer but also to form an electrode pattern.
Patent Literature 4, for example, discloses a method for forming an electrode pattern, the method (i) aligning, in a mask equivalent in size to a substrate, short-diameter holes or long and narrow slit pores in a direction which intersects a direction in which the mask is shifted and (ii) performing vapor deposition of an electrode material while the mask is shifted in a direction in which the short-diameter holes or slit pores are aligned.
In the vacuum vapor deposition method involving a shadow mask as described above, the shadow mask is fixed (for example, welded) to a mask frame under tension for prevention of, for example, bending and distortion.
Such a conventional selective vapor deposition method requires a mask to be larger as a substrate becomes larger. A larger mask, however, is likely to cause a gap, whose size varies depending on a position on the vapor-deposited surface of the substrate, between the substrate and the mask due to self-weight bending and elongation of the mask. Use of the conventional selective vapor deposition method therefore makes it difficult to perform precise patterning, thereby causing problems such as misplacement of vapor deposition and color mixture. As a result, the patterning cannot be performed with high resolution.
Moreover, a larger mask requires an increase in size and weight of members such as the mask and a frame holding the mask. This makes handling of these members difficult, thereby threatening productivity and safety. In addition, a larger mask requires a vapor deposition device and accompanying devices to become extremely large and complicated. This makes device designing difficult and makes a device installation cost expensive.
It is therefore difficult to apply the conventional selective vapor deposition method to a large-size substrate. For example, selective vapor deposition at a mass production level has not been established yet for a large-size substrate such as a 60-inch or larger substrate.
As a solution to the above problem, Patent Literature 5 proposes a method (scan vapor deposition method) in which a vapor deposition source and a shadow mask that is smaller in size than a substrate are unified and an organic film is formed in a pattern in a predetermined location on the substrate by carrying out vapor deposition while scanning the unified members or the substrate in a state in which a gap is secured between the shadow mask and the substrate. Such a scan vapor deposition method allows a shadow mask to be small, and therefore does not incur the above problem.